NavList:

On the distance side, the only scale on the transparent disk is the longitude distance family of curves with the zero "index arrow" that you align with the latitude differnce scale which is printed on the base, white, disk, alongside with the dstance scale on the white base disk. Interestingly, the longitude difference scale has curves from zero to 50 degrees with one lone point at 75 degrees to the right of the index arrow. (I shall have to try an example with that one.)

The index arm has only one scale of midlatitude running from zero near the pivot to 70 degrees near the end.

The course side has only one scale on the tranparent disk of nautical miles running from 50 to 4,000. This disk also has an "INDEX" arrow that points to the calculated course or to the "WARNING" zone. 

On the white base on the course side you find the latitude distance scale running from zero degrees 40' to 50 degrees. You also have the course scale running from zero to 45 degrees clockwise and then in reverse from 45 degrees to 89 degrees 30'. 

gl

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Gary LaPook you wrote:  There are five parts to it, a base disk, white, printed on both sides, plus transparent disks on both sides, that rotate on a central pivot, plus index arms on each side that also pivot  to align with the scales on the disks and the base.  

Thanks Gary.  I was fine on the distance side, and I could see the directions for the Course side.  I just couldn’t see which bits were free to move on the Course side.  I’d overlooked the possibility of a transparent disc.  Are you saying the inner Course scale, the one that goes from 0-45&45/90, is printed on the inner disc, the same as the D Lat scale and that the INDEX arrow and the Distance scale are printed on a transparent disc that fits over the top?  That’s very clever.  I don’t know if I dare send an OHP transparency through my laser printer without ruining it.  I think I’ll just try to make a card Distance and INDEX arrow ring to run around the Couse scale.  These cheap eBay circle cutters are very good.  We're off to Norfolk again on Sunday, so it might have to wait. DaveP